Semiconductor devices in which the conductivity of all the transistors is either n-type or p-type have been developed. In particular, development of semiconductor devices that are constituted only by n-channel transistors has been advanced (e.g., Patent Documents 1 to 4).
Such a semiconductor device includes, for example, a first transistor having one of a source and a drain connected to a power supply line and the other of the source and the drain connected to an output, and one or a plurality of second transistors connected between a gate of the first transistor and each wiring.
In order to make the amplitude voltage of an output signal from the semiconductor device equal to a power supply voltage, the potential of the gate of the first transistor is made higher (or lower) than the power supply voltage by capacitive coupling in many cases. In order to realize this, the gate of the first transistor needs to be in a floating state. For that reason, it is necessary to turn off the second transistor (or all the plurality of second transistors) connected to the gate of the first transistor.